Valve bags have been used for many years for packaging a wide variety of materials including cement and fertilizer. Valve bags are those having a small opening, smaller than the entire top of the bag, which type is generally referred to as "open top bags." Valve bags have an important advantage of easy filling through a valve structure, yet the valve may be self-closing after filling, due to the weight and volume of the filled contents. Also, valve bags are often used where the contents of the bag may be dusty and may prevent satisfactory and positive sealing of the bag. A number of prior designs for valve bags have been ones wherein the valve was a separate structure, often of a thin material, in order to provide the necessary antisift qualities to the valve after filling the bag. This separate valve structure was shown in U.S. Pat. Nos. 2,895,387; 3,394,871; and 3,221,789, and it necessitated considerable cost and complexity in the manufacture of the bags in order to insert this separate valve sleeve, position it properly, and fix it in position.
Practically all valve bags were produced as individual bags and the valve manually inserted onto a filling spout, the bag filled with the desired contents, and then removed from the spout. Often the valve was tucked inside the bag by the operator so that the valve would be closed by the weight and bulk of the contents when the bag was laid flat. These individual bags required considerable labor cost in the filling of the bags because such manual handling for filling was slow, tedious, and often dangerous if the bags were being filled with toxic or hazardous material.
U.S. Pat. No. 3,746,246 showed a valve bag not requiring any separate supplemental valve sleeve to be inserted during its manufacture, the valve being constructed from the overlapping material of the bag itself. However, the bags still were separate, individual bags which required the manual operator to deftly manipulate the valve of the bag onto the filling spout during the filling operation and manually remove the bag from the spout upon completion of the filling, and hence this was also a slow filling operation, with considerable labor expense. A similar construction was found in U.S. Pat. No. 3,833,166.
U.S. Pat. Nos. 3,559,874; 3,583,127; 3,699,746; 3,791,573; and 3,817,017 disclosed an interconnected chain of bags with a tunnel at the top edge for guidance of this chain of bags onto a mandrel of a bag-filling machine, with the bags being open-top bags for filling. In cases of powder being shipped in bags, often the bags need to be sterile so that the powder, e.g. foodstuffs, is not contaminated. If valve bags are utilized, which are often used with powdery contents, it is difficult to maintain the sterility of the interior of the bag during shipment and storage before use at a bag filling machine. This is due to the fact the valve in the bag permits a passage of air into and out of the bag, especially with changes in atmospheric pressure. Where the bag is being shipped or stored in non-sterile conditions, which is the usual case, this can seriously affect the sterile condition of such bags.
Accordingly, the problem to be solved is how to provide a bag in a series of interconnected bags so that the bags are provided with valves, so that they may be filled on an automatic bag filling machine rather than by manual filling, and so that the bag valve is closed during shipment and storage in order to minimize contamination inside the bags, or even to maintain sterility inside the bags.